In a small bowl, mix together ½ teaspoon Italian seasoning, salt, and pepper. Evenly season the chicken with the mixture.
To a large skillet over medium heat, add oil. Once the oil is hot, add the seasoned chicken to the skillet. Cook for 7-8 minutes, turning occasionally, until golden brown and fully cooked to an internal temperature of 165°F.
Transfer the cooked chicken to a plate and tent with aluminum foil to keep warm.
In the same skillet over medium heat, melt butter. Add garlic and cook for 1-2 minutes.
Pour in the chicken broth, scraping up any browned bits from the bottom. Let it simmer for 2-3 minutes.
Reduce heat to medium-low. Stir in heavy cream and cream cheese, whisking until smooth.
Gradually add the Parmesan cheese, stirring continuously to avoid clumping.
Stir in the remaining ½ teaspoon Italian seasoning, sun-dried tomatoes, and red pepper flakes (if using). Simmer for 3-4 minutes, or until the sauce slightly thickens.
Add the tortellini directly into the sauce, stirring to coat. Let it simmer for 5-6 minutes, stirring occasionally, until the pasta is tender and absorbs the sauce.
Return the cooked chicken and spinach to the skillet, stirring to combine. Let it simmer for 2-3 more minutes until the spinach is wilted.
Remove from heat and sprinkle with fresh basil for garnish. Serve hot.